Molten Metal Pressure Pour Furnace

ABSTRACT

An apparatus and process are provided for discharging a dose of a molten metal from a pressure pour furnace. A heating chamber of the furnace is used to keep the molten metal at a selected temperature. A sealing port between the heating chamber and a pressure chamber allows selectively filling of the pressure chamber with molten metal from the heating chamber by inserting or removing a sealing means from the sealing port. The sealing means inserted in the sealing port also provides a means for preventing back flow of the molten metal to the heating chamber when the pressure chamber is pressurized. Differential pressure sensing of the pressure of the molten metal in the pressure chamber and the pressure of the pressurizing gas in the pressure chamber can optionally be used to achieve an accurate measured discharge from the pressure chamber as the level of molten metal decreases from repeated discharges of doses from the furnace. The sealing plate in which the sealing port is disposed and the sealing means selectively inserted or removed from the sealing port can be used as a metering valve between two molten metal containing components such as a launder and a pressure chamber of a pressure pour furnace.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of application Ser. No. 11/862,735,filed Sep. 27, 2007, which is a divisional application of applicationSer. No. 10/382,150, filed Mar. 5, 2003, now U.S. Pat. No. 7,279,128,which application claims the benefit of U.S. Provisional Application No.60/410,408, filed Sep. 13, 2002, and U.S. Provisional Application No.60/413,183 filed Sep. 24, 2002, all of which applications areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to molten metal pressure pourfurnaces, and in particular, to such furnaces wherein a repeatedlyprecise dose of molten metal is discharged from the furnace. The presentinvention further relates to a molten metal flow valve that can be usedwith molten metal pressure pour furnaces.

BACKGROUND OF THE INVENTION

Pressure pour or dosing furnaces can be used to discharge repeated andmeasured doses of a molten metal from the furnace for filling acontinuous line of molds. The opening to the sprue of a mold is broughtin contact with the outlet of the furnace and a gas is used to exertpressure on the molten metal in the furnace, which forces a measureddose of the melt into the sprue, through the gating system and into themold cavities. Molds can be sequentially filled in the process.

U.S. Pat. No. 4,220,319 to Rohmann discloses a single chamber pressurepour furnace. A metered discharge from the furnace is accomplished bydifferential pressure sensing of air in the pressurized chamber. Thepressure at which molten metal in the chamber rises to the end of theoutlet tube prior to each discharge is sensed. This pressure reading isused as the baseline pressure at the start of a pour. The pour isterminated by release of pressure in the chamber when the chamberpressure reaches a selected value.

U.S. Pat. No. 5,477,907 to Meyer et al discloses a pressure chamber thatis isolated from a heating chamber by a wall with an opening through it.A backloading air regulator is used to account for the pressure increasein the pressure chamber that is required for the molten metal to rise tothe end of the outlet tube before the timed period of discharge isstarted. Further backflow of molten metal into the heating chamber isallowed through the opening in the wall when the pressure chamber ispressurized.

U.S. Pat. No. 5,913,358 to Chadwick discloses the use of a non-returnvalve in the wall between the pressure chamber and heating chamber toprevent the backflow of molten metal when the pressure chamber ispressurized. The non-return valve is disclosed typically as a ball andsocket valve that acts automatically to prevent reverse flow. Apotential disadvantage of this arrangement is that the molten metal, orparticulate in the melt, could lodge the ball in a position thatpermanently blocks flow of the molten metal from the heating chamber tothe pressure chamber as required to replenish the supply of melt in thechamber.

U.S. Pat. No. 5,590,681 to Schaefer et al. discloses a plug valveassembly integral with upstream and down stream launder sections. Theupstream launder section is connected to a low pressure casting furnace,and the upstream launder section is connected to a supply of moltenmetal. Flow between the supply and the low pressure casting furnace iscontrolled by the plug valve assembly.

One object of the present invention is to provide a pressure pourfurnace wherein the pressure differential between the molten metal at aselected level in the pressure chamber and the pressurized gas used toperform a pressure pour in the pressure chamber is used to provide arepeatedly precise measured discharge of melt from the furnace. Anotherobject of the present invention is to control the flow of molten metalto the pressure chamber of a pressure pour furnace with a compactmetering valve arrangement that will also provide an efficient method ofblocking backflow of the molten metal from the pressure chamber into theheating chamber, or metal supply chamber, when the pressure chamber ispressurized.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention is an apparatus for, and method of,discharging a dose of molten metal, or melt, from a furnace comprising areceiving chamber, heating chamber and pressure chamber. Molten metal issupplied to the receiving chamber; maintained at a desired temperaturein the heating chamber; and discharged from the pressure chamber. Asealing plate having a sealing port in it is disposed between theheating chamber and the pressure chamber to control the flow of meltfrom the heating chamber to the pressure chamber by the insertion orremoval of a sealing means in the sealing port. Insertion of the sealingmeans in the sealing port also prevents the back flow of melt from thepressure chamber to the heating chamber when the pressure chamber ispressurized. A gas injected into the pressure chamber is used to forcethe melt from an outlet dosing tube in the pressure chamber and into asuitable container. The dosing tube may be extend from the pressurechamber for connection with a mold for filing and retracted into thepressure chamber after the mold is filled. In one example of theinvention, the means for blocking the back flow of melt from thepressure chamber to the heating chamber is a sealing means thatsubstantially blocks the back flow of melt through the sealing port in acomposite high thermal conductivity ceramic sealing plate and port.

In another aspect, the present invention is a system for deliveringdoses of molten metal from one or more molten metal pressure pourfurnaces when the molten metal is supplied from one or more metalmelting furnaces by a launder network. One or more heat treatmentprocesses may be performed on the molten metal before being delivered tothe metal pressure pour furnaces by the launder network.

In another aspect, the present invention is a metering valve that can beformed from a sealing plate that prevents the flow of molten metalbetween two adjoining molten metal containing components such as alaunder and the pressure chamber of a pressure pour furnace. The sealingplate has a sealing port disposed in it to allow the flow of moltenmetal when a sealing means is not inserted in the sealing port and toprevent the flow of molten metal when the sealing means is inserted inthe sealing port.

These aspects of the invention are further set forth in thisspecification, and other aspects of the invention are as set forth inthis specification.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is a cross sectional view of one example of the molten metalpressure pour furnace of the present invention.

FIG. 2 is a top view of one example of a pressure chamber used in amolten metal pressure pour furnace of the present invention.

FIG. 3 is a cross sectional view of the pressure chamber illustrated inFIG. 2 at line A-A.

FIG. 4 is a cross sectional view of the pressure chamber illustrated inFIG. 2 at line B-B.

FIG. 5 is a partial cross sectional view of the pressure chamberillustrated in FIG. 4 with the additional feature of a double bellowsarrangement around the dosing tube.

FIG. 6( a) illustrates one example of a metering valve used to controlflow of a molten metal between adjoining molten metal containingcomponents.

FIG. 6( b) and FIG. 6( c) illustrate one example of a dosing tube anddosing tube assembly used in the pressure chamber of a molten metalpressure pour furnace of the present invention.

FIG. 7 diagrammatically illustrates one example of an integratedarrangement of molten metal supply sources, molten metal heat treatmentvessels and the molten metal pressure pour furnaces of the presentinvention.

FIG. 8( a) through FIG. 8( h) is a flowchart of an example of a controlprocess that can be used for the molten metal pour furnace of thepresent invention.

FIG. 9( a) illustrates a metering valve of the present invention that isused to regulate the flow of a molten metal into a low pressure pourfurnace.

FIG. 9( b) diagrammatically illustrates an integrated arrangement ofmolten metal supply sources, molten metal heat treatment vessels and aplurality of the metering valves of the present invention that are usedto regulate the flow of a molten metal into a plurality of low pressurefurnaces.

FIG. 10( a) illustrates a double metering valve arrangement of thepresent invention that is used to regulate the flow of a molten metalinto a low pressure pour furnace.

FIG. 10( b) diagrammatically illustrates an integrated arrangement ofmolten metal supply sources, molten metal heat treatment vessels and aplurality of the double metering valve arrangements of the presentinvention that are used to regulate the flow of a molten metal into aplurality of low pressure furnaces.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like numerals indicate likeelements, there is shown in the drawings, one example of the moltenmetal pressure pour furnace 10 of the present invention. The furnacecomprises a receiving chamber 12, heating chamber 14 and pressurechamber 16. The furnace's exterior support structure 18 is formed from asuitable material such as a mild steel, and may be lined with a suitablerefractory 20 such as multicomponent refractory materials as known inthe art. As explained in further detail below: receiving chamber 12 issupplied with molten metal, or melt, from a suitable source; heatingchamber 14 maintains the melt at a suitable temperature; and pressurechamber 16 discharges a measured dose of melt from the furnace. Whenfurnace 10 provides molten metal to a continuous line of molds, thepressure chamber usually holds a sufficient quantity of melt for fillingmultiple molds in succession. When required the molten metal in thepressure chamber is replenished with melt from the heating chamber.Molten metal load line 11 (shown as a dashed line) in FIG. 1 illustratesa typical fully loaded furnace.

Receiving chamber 12 can be supplied with molten metal, such as, but notlimited to, a liquid aluminum composition, by a suitable pumping systemor launder. In one example of the invention, the supply of melt isprovided by a launder delivery system connected to a melt and metaltreatment system wherein the launder delivery system maintains asubstantially constant level of molten metal in the receiving chamber.For example, aluminum ingots and scrap may be melted in a stack furnaceto produce liquid aluminum that is collected in a holding furnace. Theliquid aluminum may be further treated to remove hydrogen gas, oxides,impurities and other active metals in a filtering vessel that is fedfrom the holding furnace. Either a gravity feed or pumped launderdelivery system may be connected between the holding furnace orfiltering vessel and receiving chamber 12. A means for sensing the levelof molten metal in the receiving chamber or launder delivery system,such as a laser sensing system or mechanical float switch, can be usedto sense the level of melt for control of the flow of molten metal fromthe holding furnace or filtering vessel to the receiving chamber so thata substantially constant height of melt is continuously maintained inthe receiving chamber. Receiving chamber 12 may also include means fordegassing the melt in the chamber, such as a carbon diffusion lance,floor purge plugs or a rotary dispersion lance top, as used to injectchlorine gas, nitrogen or argon into liquid aluminum. Further thelaunder delivery system may be arranged so that a single supply of meltis distributed to a plurality of pressure pour furnaces.

Heating chamber 14 is partially separated from receiving chamber 12 byfurnace arch 23 which is formed from a suitable refractory composition.Heating chamber 14 includes suitable means for heating melt in thechamber, such as electric heating elements 20, or fossil fuel firedburners. Fossil fuel fired burners are less advantageous in thatcombustion gas byproducts may contaminant melt in the heating chamber.Suitable resistive electric heating elements are preferably of a highwatt density type such as those formed from a silicon carbidecomposition. Furnace arch 23 serves as a means for retaining heat and aprotective atmosphere within the heating chamber, and prevents any meltperturbations in the receiving chamber from propagating into the heatingchamber. Normally the heights of the melt in the receiving and heatingchambers are the same. Heating elements 20 are a part of a furnaceheating system that maintains a pre-selected temperature of the moltenmetal in the heating chamber. One or more means for sensing temperatureof the melt in the furnace, such as immersed thermocouple 21 is used asan input to a processing means, such as a programmable logic controller(PLC). The processing means provides an output signal to the means forheating the molten metal in the heating chamber. For example, ifelectric resistive heating elements are used, the output signal may beused to control the switching of silicon controlled rectifiers (SCRs) inan SCR heater controller. Temperature sensing may include differentialtemperature sensing of the molten metal in the receiving and heatingchambers. Preferably heating chamber 14 includes a non-reactive gaspurging system wherein a gas, such as nitrogen, is used to purge the airabove the surface of the molten metal in the heating chamber to minimizethe formation of oxide on the surface, and minimize the diffusion ofcontaminants into the molten metal, such as hydrogen gas in liquidaluminum. Optionally porous floor plugs may also be provided in theheating chamber to purge contaminants in the molten metal, such ashydrogen gas in aluminum, by flowing a non-reactive gas, such asnitrogen or argon, through the melt.

Pressure chamber 16 is separated from heating chamber 14 by a compositesealing plate and port 22 as best illustrated in FIG. 6( a). In onenon-limiting example of the invention, the composite sealing plate andport is integrally cast from a high thermal conductivity ceramic such asa nitrite bonded silicon carbide or other ceramic composition. Use ofsuch composition is desireable for retaining adequate heat content inthe melt in the pressure chamber. Alternatively, the sealing port may beseparately fabricated and attached to the sealing plate. The portprovides a means for flow of melt from the heating chamber to thepressure chamber. A sealing means for insertion into the sealing portsubstantially blocks the back flow of molten metal from the pressurechamber to the heating chamber through the port when the pressurechamber is pressurized, as well as blocking flow of the molten metalfrom the heating chamber to the pressure chamber. The top of pressurechamber 16 is substantially sealed from the ambient environment by asuitable wall or lid 26 and seals around penetrating openings forelements as further described below. The lid may be fabricated from amild steel plate that is suitably fastened to the pressure chamber.

The means for substantially blocking the back flow of molten metal fromthe pressure chamber to the heating chamber comprises a sealing meansinserted into the sealing port. In this non-limiting example of theinvention, the sealing means comprises sealing element 30 a at one endof sealing tube 30, wherein sealing element 30 a is generallyhemispherical in shape and seats into a generally conically-shapedsealing port to substantially block the back flow of molten metal fromthe pressure chamber when the pressure chamber is pressurized as furtherdescribed below. The sealing tube and element may be cast from aheat-resistant and wear-resistant material, such as a nitrite bondedsilicon carbide or other ceramic composition.

As shown in the non-limiting example of the metering valve of thepresent invention in FIG. 6( a), sealing port 22 comprises asubstantially conically-shaped section at one end of the port with itslongitudinal axis generally vertically aligned. The smaller diameter endof the conically-shaped section is connected to a substantiallycylindrically-shaped section that is elbow-shaped so that thesubstantially vertical flow of the melt through the conically-shapedsection of an open sealing port is redirected to a substantiallyhorizontal flow at the other end of the sealing port. Conversely flow inthe opposite direction first flows through the elbow-shaped section andthen through the conically-shaped section of the sealing port. Thesealing port is integrally attached to sealing plate 25 in thisparticular example of the invention. Sealing plate 25 serves as thebarrier between two adjoining molten metal containing elements.

Sealing port 22 and the sealing means for allowing or preventing flow ofthe melt through the port comprise a metering valve that generallycontrols the flow of melt to adjoining molten metal containing elements.In this particular application, the adjoining molten metal containingelements are the heating chamber and the pressure chamber of a moltenmetal pressure pour furnace.

Dosing tube 32 extends obliquely through wall or lid 26 into the moltenmetal in the pressure chamber and serves as a means for discharging ametered amount of melt from the pressure chamber. In other examples ofthe invention the orientation of the dosing tube relative to the topwall of the furnace may be different. As shown in FIG. 3, dosing tubesealing bellows 34 surrounds the external end of the dosing tube toprovide a pressurized seal around the opening in lid 26 through whichthe dosing tube penetrates. Use of the bellows allows the pressure sealto be maintained as the dosing tube is extended out of or retracted intothe pressure chamber as further described below.

FIG. 6( b) and FIG. 6( c) illustrate another example of the dosing tube32 and dosing tube assembly, respectively, of the present invention. Inthis arrangement, three powered cylinders 33 (one not visible in thedrawing) are used to extend and retract dosing tube 32. Bellows 34extend and retract with the dosing tube to retain the pressurized sealaround the dosing tube opening in the wall of the pressure chamber. Asfurther explained below pressure plate 35 makes contact with the surfaceof a mold when the dosing tube is extended. External end 32 b of dosingtube 32 inserts into the sprue of a mold when the dosing tube isextended.

Immersion tube heater 36 can be optionally provided to heat melt in thepressure chamber if necessary to compensate for the loss of heat fromthe melt in the pressure chamber. The auxiliary heater may comprise aresistive silicon carbide heating element disposed within a siliconnitrite tube that penetrates through lid 26 into the molten metal. Athermocouple within the tube can be used to protect against overheatingof the heating element. Immersion temperature sensing device 37, such asa high thermal conductivity silicon nitride thermocouple, is used as asensor for regulating the output of heater 36.

As best seen in FIG. 4, means for pressurizing the molten metal in thepressure chamber is provided by injecting a gas (such as dry air, argonor nitrogen) from a suitable supply 41, under pressure, through gas port38 located above the surface level of the melt. A means for sensing thedynamic pressure on the molten metal at a pre-selected height in thepressure chamber can be provided by melt pressure sensing tube 40 andmelt pressure sensor 42. One non-limiting method of sensing the meltpressure is to bubble a non-reacting gas, such as nitrogen or argon,through the tube at a pressure sufficient to prevent the melt fromrising in the melt pressure sensing tube and release a bubble at apredetermined rate. A means for sensing the gas pressure of the gasinjected into the dosing chamber can be provided by gas pressure sensingtube 44 and gas pressure sensor 46. Gas exhaust port 43 is provided forcontrolled release of gas from the pressure chamber to ambient airduring the pour process or to depressurize the chamber.

In one non-limiting method of operation, the pressure chamber issubstantially filled with melt from the heating chamber to a heightequal to the height of the melt in the heating chamber by raisingsealing tube 30 with a suitable actuator so that sealing element 30 aunseats from the sealing port to allow the flow of melt from the heatingchamber to the pressure chamber. Sealing tube bellows 29 provides apressurized seal around the opening through which the sealing tubepenetrates into the pressure chamber and allows maintaining the seal asthe sealing tube is raised or lowered. After filling the pressurechamber, sealing tube 30 is lowered so that sealing element 30 a seatsin the sealing port to substantially block the back flow of melt intothe heating chamber as illustrated in FIG. 3. Optionally a heatingelement may be provided in sealing element 30 a to melt any molten metalthat may freeze in the sealing tube.

In some examples of the invention, gas is initially injected into thepressure chamber to force melt in the chamber up the dosing tube toapproximately the external end of the riser tube. This level of melt,which is referred to as the “ready level” is used as a reference pointfor the start of every pour from the pressure chamber. The ready levelfor a particular application may be any height of melt in the dosingtube that is suitable for the process. A means for sensing the presenceof the melt at the external end of the riser tube is provided. In oneexample of the invention, the means comprise a pair of low voltageelectrically conducting probes 48 that form a normally open circuit whenthey are not immersed in molten metal, and a closed circuit when theyare immersed in molten metal to indicate that the melt is at theexternal end of the riser tube. A means is provided to move the probesout of the opening of the riser tube. In this example, the meanscomprise pivot arm 50, which is shown in the lowered and raised (dashedlines) positions in FIG. 3. In alternate examples of the invention alaser sensor may be used as the means for sensing the presence of themelt at the external end of the riser tube.

Once the melt is raised to the external end of the dosing (riser) tube(or other melt ready level), the opening of a container, such as theopening in a mold sprue, is brought into the vicinity of the externalend of the riser tube, with the center of the sprue openingapproximately aligned with the center of the opening in the riser tube.Dosing tube 32 is extended out of the pressure chamber by means of asuitable actuator so that a substantially pressurized seal is achievedbetween the end of the riser tube and the opening in the mold sprue.Dosing tube sealing bellows 34 expands to maintain the pressure sealaround the opening through which the dosing tube penetrates when thetube is in its extended position. In some examples of the invention, adouble dosing tube bellows arrangement can be used as illustrated inFIG. 5. First dosing tube bellows 34 a provides a pressurized sealaround the dosing tube opening in lid 26. Suitable actuators 90 a and 90b, preferably hydraulic cylinders due to the proximity to molten metal,are used to extend or retract the dosing tube while first dosing tubebellows 34 a expands or contracts to maintain the seal. Other types ofactuators, such as hydraulically or electrically driven actuators, mayalso be used. Second dosing tube bellows 34 b compresses as the end ofthe dosing tube seals around the opening in the mold sprue to absorb anyexcess pressure exerted by the mating mold surface.

A requisite amount of gas is injected into the pressure chamber todischarge a measured dose of melt into the mold. The volume and timerate of gas injection can initially be established by an algorithm usedby the processing means. After pressure pouring the desired amount ofmolten metal into the mold, the riser tube is retracted into thepressure chamber by means of a suitable actuator. The molds are indexedby moving the filled mold and placing an empty mold in its place.Between mold transitions, probes 48 can be repositioned into the end ofthe dosing tube to pressurize the pressure chamber to the level requiredto bring the melt back up to the end of the dosing tube. The empty moldis then filled by the process as described above for the previous mold.

Typically a filled pressure chamber can be used to fill a number ofmolds, after which the level of melt in the pressure furnace drops to alevel that requires replenishment of the melt in the pressure chamberfrom the heating chamber. One non-limiting method of level sensing ofthe melt in the chamber can be accomplished as a function of the appliedgas pressure in the chamber since increasing applied gas pressure isproportional to the level of melt in the chamber. When replenishment isrequired, sealing tube 30 is raised to allow a refill of the pressurechamber. Gas exhaust port 43 is normally open when melt flows from theheating chamber to the pressure chamber through the sealing port duringa refill. In alternative examples of the example, vacuum pump 92 can beused to draw a vacuum on the pressure chamber to increase the refillflow rate through the sealing port. This is of particular advantage whena slower refill rate will not support a fast indexing speed of molds. Inother examples of the invention, a gas may be injected under pressureinto the volume above the melt in heating chamber 14 to increase therefill flow rate through the sealing port. If the heating chamberincludes the optional non-reactive gas purging system as describedabove, the purging system may include means for gas pressurizing themelt in the heating chamber. Pressurization of the melt in the heatingchamber for increased refill flow rate may optionally be combined withvacuum draw on the pressure chamber. When the melt in heating chamber 14is under pressure, furnace arch 23 seals the gas volume in the heatingchamber from ambient air pressure. In alternate examples of theinvention, means may be provided for sealing receiving chamber fromambient air pressure when melt in the heating and/or receiving chamberis pressurized with a gas.

Use of the differential pressure method in some examples of theinvention enables accurate control of the measured dose from the risertube as the quantity of melt in the pressure chamber reduces and themagnitude of applied pressure must increase. The algorithm for pressurecontrol may be adaptively adjusted for future pours into the same typeof mold by feedback of the sensed differential pressure during theprevious pour.

FIG. 8( a) through FIG. 8( h) illustrate one non-limiting example of aprocess control flowchart routine that can be used to discharge moltenmetal from a pressure pour furnace of the present invention. The processcontrol routine can be programmed by one skilled in the art forexecution by a suitable processor and supporting computer hardware andsoftware, and input and output control devices. Starting on FIG. 8( a),with pressure chamber 16 vented to atmosphere, sealing port 22 open, andthe pressure chamber filled with melt, subroutine 102 is executed toenergize the sealing tube close actuator. The sealing tube closeactuator may be any suitable drive device for inserting sealing element30 a into the sealing port. In this particular example of the invention,the sealing tube actuator is pneumatically driven cylinder 27. While thesealing element is moving to a seated position in the sealing port,subroutine 104 is executed to sense whether there is a blockage in thesealing port that prevents the sealing element from properly seating inthe sealing port. Blockage can be sensed by back force loading (in thisexample, back air pressure) on the sealing tube actuator. If a blockageis sensed, subroutine 106 activates a back pressure stop alarm that canbe arranged to stop the process operation and alert an operator to theabnormal condition for correction of the abnormal condition. The sealingelement continues to move into the sealing port until subroutine 108senses that the sealing port closed limit switch has been activated. Thesealing port closed limit switch may be a mechanical limit switchmounted on the sealing tube assembly external to the pressure chamber.The sealing port closed limit switch changes state when the sealingelement has completed full travel into the sealing port and thede-energize sealing tube close actuator subroutine 110 is executed tostop the actuator. At this time, subroutine 112 may be executed to makea check of all systems alarms, such as a low temperature alarm for meltin the pressure chamber. If any alarm flag is in the alarmed state, thensubroutine 114 activates a safety stop switch and subroutine 118provides an appropriate alarm indication to the operator. Afterappropriate operator action, subroutine 120 clears the alarm, and theoperator de-activates the safety stop switch so that subroutine 121 canreturn to the main process routine. If the alarm status is clear, thensubroutine 122 is executed to seal the pressure chamber from atmosphericpressure. This can be accomplished by closing gas exhaust port 43 andinjecting gas into the pressure chamber from gas supply 41

Gas is injected into the pressure chamber until the melt is raised indosing tube 32 to a level that is designated as the “ready level”.Alternative, and possibly a combination of, methods may be used to sensethe melt reaching the ready level. As illustrated in FIG. 8( c) onemethod is by laser sensing of the height of the melt in the dosing tube.The laser source is mounted external to the pressure chamber and thelaser beam is aimed at the opening of the dosing tube. Subroutine 126executes repeated measurements of the laser beams “bounce back” time offof the surface of the melt in the tube to determine the height of themelt in the dosing tube. When the height reaches the designated readylevel, subroutine 132 holds the gas pressure at the melt ready level.Alternatively, or in combination with laser sensing, subroutine 128 canexecute a “bubble tube” ready level sensing. Bubble tube ready levelsensing involves slowly injecting a gas down melt pressure sensing tube40 until melt pressure sensor 42 senses a slow pulse rate (e.g.,approximately one pulse per second) air supply, which indicates a slowbubble release of the gas into the melt at the end of the sensing tube40 immersed in the melt. The pressure at that point in the melt iscalibrated to the bubble release rate, and the ready level of melt inthe dosing tube can be calculated in subroutine 128 from this pressure,the geometry of the pressure vessel and the volume of melt discharged ineach dose of melt from the furnace. When the bubble tube ready levelsensing rate indicates the designated ready level, subroutine 132 holdsthe gas pressure at the melt ready level. Alternative to the lasersensing method is wire probe sensing of the ready level. For this methodsubroutine 130 moves conducting probes 48 into the external end of thedosing tube so that the tips of the two unconnected probes are at themelt ready level. When melt rises up to the tips of the two probes, themelt completes an electrical circuit that outputs a signal indicatingthat the ready level has been reached. At this point subroutine 132holds the gas pressure at the melt ready level.

With melt held at the ready level in the pressure chamber, subroutine133 is executed to sense whether a mold has been indexed for filing bythe mold line machinery. When subroutine 133 receives a signal from themold line machinery that a mold has been indexed for filing, subroutine134 energizes the dosing tube extend actuator. The dosing tube extendactuator may be any suitable drive device for extending the dosing tubefor mating with the sprue of a mold. In the example of the inventionshown in FIG. 6( c), the sealing tube actuator is three pneumaticallydriven cylinders 33. The dosing tube continues to extend toward thesurface of the indexed mold until subroutine 136 senses that the end ofthe dosing tube has made contact with the mold to ensure a sufficientseal between the end of the dosing tube and the sprue of the mold sothat there is no leakage of melt from the connection when melt isinjected into the sprue of the mold. Pressure sensing can beaccomplished by utilizing a pressure load sensor behind pressure plate35 in the non-limiting example of the invention shown in FIG. 6( c).When the sensed pressure reaches a preset level for sufficient sealing,de-energize dosing tube extend actuator subroutine 138 is executed tostop the actuator.

Subroutine 140 injects more gas into the pressure chamber in accordancewith a predetermined mold fill profile. For example, one or morepressure levels over discrete time periods may be achieved during a moldfill profile according to mold configurations and the remaining amountof melt in the pressure chamber. Once the mold fill profile has executedsubroutine 142 initiates subroutine 144 to release gas from the pressurechamber and return the melt in the chamber to the ready level. Asillustrated in FIG. 8( f) bubble tube ready level sensing subroutine148, as previously described, may be used to determine when the melt hasreturned to ready level. Subroutine 150 holds the melt at the readylevel. In addition to bubble tube sensing, after the mold line machinerymoves the indexed filled mold away from the external end of the dosingtube and before the next unfilled mold is moved into the indexedposition for fill, laser sensing and/or wire probe sensing may be usedin lieu of bubble tube ready level sensing, or as a supplement to bubbletube ready level sensing.

Subroutine 152 determines whether a refill (recharge) of melt in thepressure chamber is required. Typically this is predetermined based uponthe volume of the cavities in the molds being filled and the capacity ofthe pressure chamber. However, in other examples of the invention, adirect means of sensing the level of melt in the pressure chamber may beutilized. If a recharge is not required, subroutine 154 energizes thedosing tube retract actuator. The dosing tube continues to retract awayfrom the surface of the indexed mold until subroutine 156 senses thatthe dosing tube has fully retracted, when subroutine 158 de-energizesthe dosing tube retract actuator. Full retraction of the dosing tube maybe accomplished by the use of a mechanical limit switch on the externaldosing tube assembly. Execution of subroutine 160 blows a stream of airacross the external opening of the dosing tube to remove any remnant ofmelt from the mold fill, and subroutine 162 sends a signal to the moldline machinery that the indexed mold has been filed. At this point theprocess returns to subroutine 133 on FIG. 8( d) to wait for the nextempty mold to be indexed for filing from the furnace.

If subroutine 152 determines that a recharge of melt in the pressurechamber is required, as illustrated in FIG. 8( h), while subroutines164, 166, 168, 170 and 172 are being executed for retracting the dosingtube and sending an indexed mold filled signal to the mold linemachinery, subroutine 174 brings the pressure chamber to atmosphericpressure, for example, by opening gas exhaust port 43. Then subroutine176 is executed to energize the sealing tube open actuator. The sealingelement continues to move away from the sealing port until subroutine178 senses that the sealing port opened limit switch has been activated.The sealing port opened limit switch may be a mechanical limit switchmounted on the sealing tube assembly external to the pressure chamber.The sealing port opened limit switch changes state when the sealing tubeelement has fully moved to the open position and the de-energize sealingtube open actuator subroutine 180 is executed to stop the actuator.Ideally when the sealing port 22 is opened, melt will flow into thepressure chamber until it reaches a melt level equal to that in theheating chamber. However, the speed of the mold line machinery may indexan empty mold for filling before a complete refill of the pressurechamber, and in order to not delay the rate of mold filling, a less thanfull recharge of the pressure furnace may be accomplished. Subroutine184 determines whether the recharge of the pressure chamber is complete.The determination may be based upon the amount of time that the sealingport is open, or in other examples of the invention, direct sensing ofthe melt level in the pressure chamber may be utilized. Subroutine 184passes process control to subroutine 102 in FIG. 8( a) when recharge ofthe pressure chamber has been accomplished, and the mold filing processcontinues. In some examples of the invention, extension and retractionof the dosing tube is not required if the dosing tube is feeding a fixedlaunder as further described below. For these examples of the invention,the non-limiting example of a process control of the present inventionillustrated in FIG. 8( a) through FIG. 8( h) are suitably modified toaccommodate a fixed dosing tube.

Alternative examples are contemplated within the scope of the invention.For example, rather than pressure discharging the measured melt directlyinto a mold from furnace 10, the discharge may be to an intermediatereservoir from which a container is filled by gravity release of meltfrom the reservoir. Alternatively the discharge may be to a launder thatgravity feeds the molten metal into a mold. In some examples of theinvention it may not be necessary to extend and retract the dosing tube.In these examples, the dosing tube sealing bellows may or may not beused. Further contemplated within the scope of the invention is thedisclosed features of the pressure chamber in combination with a heatingchamber and/or a receiving chamber of various configurations.

FIG. 7 diagrammatically illustrates one example of an integratedarrangement of molten metal supply sources, M₁ through M_(n) feeding asupply launder distribution network 52 a, that can be optionallyconnected to a furnace launder distribution network 52 b via one or moremetal treatment vessels (MT), or directly to the furnace launderdistribution network. The molten metal supply sources can be metalmelting furnaces, such as vertical stack scrap and/or ingot aluminum, orother metal charge, melting furnaces, as known in the art. The metaltreatment vessels provide a means for treating the molten metal outputfrom the melting furnaces, such as the removal of hydrogen gas, oxides,impurities and other active metals in the molten metal, as known in theart. The furnace launder distribution network 52 b supplies the moltenmetal to a plurality of molten metal pressure pour furnaces 10 of thepresent invention (designated DF₁ through DF_(n) in FIG. 7). Moltenmetal pressure pour furnaces 10 discharge doses of the molten metal asdescribed herein. Mold transport machinery 94 is diagrammaticallyillustrated with exemplar molds 96 being transported to and from eachfurnace for sequential indexing in position (mold 96 a) for filling frompressure pour furnace 10. The launder distribution networks aretypically configured as an open heated trough and can be arranged forgravity flow of the molten metal from the supply source to the moltenmetal pressure pour furnaces.

The metering valve of the present invention may also be used to controlthe flow of a molten metal between any adjoining molten metal containingcomponents other than the heating chamber and pressure chamber of amolten metal pressure pour furnace. For example, FIG. 9( a) illustratesmetering valve 64 of the present invention comprising a sealing port 22and sealing means, such as sealing element 30 a at one end of sealingtube 30. In this arrangement of the invention the adjoining molten metalcontaining components are launder 52 and pressure chamber 56 of lowpressure molten metal furnace 54. Opening 19 in a wall of the pressurechamber is generally aligned with the outlet of sealing port 22. Thelaunder is typically an open channel using gravity flow of molten metalto the pressure chamber, but may also be an enclosed component andemploy other means for achieving the flow of molten metal. The laundermay be heated (e.g., by electric heating elements) to keep the moltenmetal in it at a desired temperature. In a low pressure melt furnace,the melt is displaced vertically upwards through supply tube 58 and intothe cavities of mold 62, which is indexed on top of the pressure chamberby mold line machinery (not shown in the drawing). Melt in the pressurechamber is forced up the supply tube by injecting a gas at a lowpressure into gas port 60. A low pressure is used so that the mold'scavities fill slowly upwards to ensure that there is no entrained air inthe die. After one or more molds are filled in this manner, the melt inthe pressure chamber must be replenished. Sealing port 22 of meteringvalve 64 is opened by removing sealing element 30 a from the sealingport as previously described, after the pressure chamber has beendepressurized. Melt from launder 52 flows through the sealing port andinto pressure chamber 56 through opening 19, preferably until the levelof the melt in the pressure chamber is at the same level as it is in thelaunder. This level is illustrated by molten metal load line 61 in FIG.9( a) (shown as a dashed line). Upon recharging pressure chamber 56 withmolten metal, the metering valve is closed by inserting sealing element30 a in the sealing port as previously described above. Since generallyin this example of the invention, metering valve 64 does not protrudeinto a pressurized chamber, bellows 29 is an optional component. Sealingplate 25 in this non-limiting example of the invention, is shown as aseparate element that is attached to a wall of connecting low pressurechamber 56. In other examples of the invention, the sealing plate may beincorporated into the connecting wall of the low pressure chamber, andthe cylindrical end of sealing port 22 of metering valve 74 would opendirectly into the interior of the pressure chamber, rather than throughintervening opening 19. FIG. 9( b) diagrammatically illustrates anintegrated arrangement of molten metal supply sources, M₁ through M_(n)feeding a supply launder distribution network 52 a, that can beoptionally connected to a furnace launder distribution network 52 b viaone or more metal treatment vessels (MT), or directly to the furnacelaunder distribution network. The furnace launder distribution network52 b supplies the molten metal to a plurality of low pressure furnaces,LPF₁ through LPF_(n). The flow of molten metal to each low pressurefurnace is controlled by a metering valve 64. Mold transport machineryis diagrammatically illustrated by dash lines 66. The mold transportmachinery line delivers empty molds to, and receives full molds from,each low pressure furnace. Mold 62 illustrates a mold indexed for fillfrom low pressure furnace LPF₁.

FIG. 10( a) illustrates an alternative method of controlling the flow ofmolten metal to a low pressure furnace. In this method a double meteringvalve chamber 68 of the present invention is used. Double metering valvechamber 68 is connected between launder 70 and pressure chamber 56 oflow pressure molten metal furnace 54. As shown in FIG. 10( a), each ofthe two metering valves, 74 and 76 in the double metering valve chambercomprise a sealing port 22 in sealing plate 25, and sealing means, suchas sealing element 30 a at one end of sealing tube 30. In this exampleof the invention, the two sealing plates form walls of the doublemetering valve chamber. Opening 19 in a wall of the pressure chamber isgenerally aligned with the outlet of the sealing port for the meteringvalve adjacent to the wall. When melt in pressure chamber 56 of moltenmetal pressure furnace 54 must be replenished, both metering valves areopened by removing sealing elements 30 a from their respective sealingports as previously described, after the pressure chamber has beendepressurized. Molten metal in the double metering valve chamber andlaunder 70 flows into pressure chamber 56 through the two open sealingports and opening 19 in the pressure chamber's wall preferably until thelevel of the melt in the pressure chamber is at the same level as it isin launder 70 and double metering valve chamber 68. This level isillustrated by molten metal load line 71 in FIG. 10( a) (shown as adashed line). Upon completion of recharging pressure chamber 56 withmolten metal, metering valve 74 is closed by inserting sealing element30 a in its sealing port as previously described above. Metering valve76 may alternatively be closed at the same time as metering valve 74, ormay remain open to allow refilling of the double metering valve chamber,after which time, metering valve 74 can be closed. Closure of meteringvalve 76 is accomplished by inserting sealing element 30 a in itssealing port as previously described above. After closure of meteringvalve 74, one or more molds are filled with melt in the pressure chamberby injecting a gas into gas port 72 to force molten metal up supply tube58 and into the cavities of mold 62 that has been indexed by mold linetransport machinery onto the top of the pressure chamber. Optionally asshown in FIG. 10( a) a gas pressure equal to the pressure applied to themelt in the pressure chamber can be applied to the melt in the doublemetering valve chamber when both metering valves 74 and 76 are closed,if required to prevent a back flow of melt into the double meteringvalve chamber. If the double metering valve chamber is not pressurized,bellows 29 is optional for each metering valve. Sealing plate 25 in thisnon-limiting example of the invention for metering valve 74 adjacent tothe wall of the pressure chamber, is shown as a separate element that isattached to a wall of connecting low pressure chamber 56. In otherexamples of the invention, the sealing plate may be incorporated intothe connecting wall of the low pressure chamber, and the cylindrical endof sealing port 22 of metering valve 74 would open directly into theinterior of the pressure chamber, rather than through interveningopening 19. FIG. 10( b) diagrammatically illustrates an integratedarrangement of molten metal supply sources, M₁ through M_(n) feeding asupply launder distribution network 52 a, that can be optionallyconnected to a furnace launder distribution network 52 b via one or moremetal treatment vessels (MT), or directly to the furnace launderdistribution network. The furnace launder distribution network 52 bsupplies the molten metal to a plurality of low pressure furnaces, LPF₁through LPF_(n). The flow of molten metal to each low pressure furnaceis controlled by a double metering valve chamber 68. Mold transportmachinery is diagrammatically illustrated in similar fashion as that inFIG. 9( b).

While each of above examples of the invention utilize a single sealingport in a sealing plate, the scope of invention includes providing morethan one sealing port in each sealing plate, with each of the sealingports having appropriate sealing means to selectively control the flowof molten metal between the adjoining molten metal containingcomponents.

The foregoing examples do not limit the scope of the disclosedinvention. The scope of the disclosed invention is further set forth inthe appended claims.

1. A method of discharging a dose of a molten metal from a pressure pourfurnace, the method comprising the steps of: venting a pressure chamberof the furnace to atmospheric pressure; opening a sealing port disposedin a wall between the pressure chamber and a heating chamber of thefurnace by removing a sealing element from the sealing port to allow theflow of the molten metal from the heating chamber through the sealingport to the pressure chamber; closing the sealing port by inserting thesealing element into the sealing port to prevent the flow of the moltenmetal from the heating chamber through the sealing port to the pressurechamber; substantially sealing the pressure chamber from atmosphericpressure; providing a dosing tube through a dosing tube opening in thepressure chamber, the dosing tube comprising a first and secondcontiguous sections, the first section disposed exterior to the pressurechamber and terminating in a dosing tube pour end, the second sectiondisposed interior to the pressure chamber and terminating in a dosingtube supply end; extending the dosing tube pour end away from thepressure chamber; and injecting a gas into the volume above the surfaceof the molten metal in the pressure chamber to force an at least onedose of the molten metal through the dosing tube and out of the dosingtube pour end.
 2. The method of claim 1 further comprising the step ofinjecting the gas above the surface of the molten metal in the pressurechamber to a ready level prior to the step of injecting the gas into thevolume above the surface of the molten metal in the pressure chamber toforce an at least one dose of molten metal through the dosing tube andout of the dosing tube pour end.
 3. The method of claim 1 wherein thesteps of opening or closing the sealing port further comprises raisingor lowering a sealing tube having a first and second opposing ends, thesealing element attached to the first end of the sealing tube, and thesecond end of the sealing tube protruding through a sealing tube openingin the wall of the pressure chamber, the sealing tube openingpressure-sealed by a bellows having a first and second opposing ends,the first end of the bellows attached to the wall of the pressurechamber around the sealing tube opening and the send end of the bellowsattached around the sealing tube external to the pressure chamber. 4.The method of claim 1 further comprising the steps of forming thesealing port from the combination of a cylindrically-shaped elbowpassage and a conically-shaped passage, and orienting the elbow passageso that the molten metal flows through the elbow passage in asubstantially horizontal path out of the heating chamber and asubstantially vertical path into the conically-shaped passage in thepressure chamber when the sealing element is removed from theconically-shaped passage.
 5. The method of claim 1 wherein the step ofextending the dosing tube pour end away from the pressure chambercomprises the steps of extending a first partial section of the firstsection of the dosing tube from the remainder of the first section ofthe dosing tube, the first partial section of the first section of thedosing tube terminating in the dosing tube pour end, and providing abellows sealing element around the first partial section and theremainder of the first section of the dosing tube.
 6. The method ofclaim 1 wherein the step of extending the dosing tube pour end away fromthe pressure chamber comprises extending the first and second sectionsof the dosing tube, and providing a bellows sealing element around thefirst section and the dosing tube opening in the pressure chamber.
 7. Amethod of providing a dose of a molten metal, the method comprising thesteps of: producing the molten metal by heating a metal charge in an atleast one metal melting furnace; supplying the molten metal to a heatingchamber of an at least one molten metal pressure pour furnace by alaunder; venting a pressure chamber of the at least one molten metalpressure pour furnace to atmospheric pressure; opening a sealing portdisposed in a wall between the pressure chamber and the heating chamberof the at least one molten metal pressure pour furnace by removing asealing element from the sealing port to allow the flow of the moltenmetal from the heating chamber through the sealing port to the pressurechamber; closing the sealing port by inserting a sealing element intothe sealing port to prevent the flow of the molten metal from theheating chamber through the sealing port to the pressure chamber;substantially sealing the pressure chamber from atmospheric pressure;providing a dosing tube through a dosing tube opening in the pressurechamber, the dosing tube comprising a first and second contiguoussections, the first section disposed exterior to the pressure chamberand terminating in a dosing tube pour end, the second section disposedinterior to the pressure chamber and terminating in a dosing tube supplyend; extending the dosing tube pour end away from the pressure chamber;and injecting a gas into the volume above the surface of the moltenmetal in the pressure chamber to force an at least one dose of themolten metal through the dosing tube and out of the dosing tube pourend.
 8. The method of claim 7 further comprising the steps of formingthe sealing port from the combination of a cylindrically-shaped elbowpassage and a conically-shaped passage and orienting the elbow passageso that the molten metal flows through the elbow passage in asubstantially horizontal path out of the heating chamber and asubstantially vertical path into the conically-shaped passage into thepressure chamber when the sealing element is removed from theconically-shaped passage.
 9. The method of claim 7 further comprisingthe step of injecting the gas above the surface of the molten metal inthe pressure chamber to a ready level prior to the step of injecting thegas into the volume above the surface of the molten metal in thepressure chamber to force an at least one dose of molten metal throughthe dosing tube and out of the dosing tube pour end.
 10. The method ofclaim 7 wherein the steps of opening or closing the sealing port furthercomprises raising or lowering a sealing tube having a first and secondopposing ends, the sealing element attached to the first end of thesealing tube, and the second end of the sealing tube protruding througha sealing tube opening in the wall of the pressure chamber, the sealingtube opening pressure-sealed with a bellows having first and secondopposing ends, the first end of the bellows attached to the wall of thepressure chamber around the sealing tube opening and the second end ofthe bellows attached around the sealing tube exterior to the pressurechamber.
 11. The method of claim 7 wherein the step of extending thedosing tube pour end away from the pressure chamber comprises the stepsof extending a first partial section of the first section of the dosingtube from the remainder of the first section of the dosing tube, thefirst partial section of the first section of the dosing tubeterminating in the dosing tube pour end, and providing a bellows sealingelement around the first partial section and the remainder of the firstsection of the dosing tube.
 12. The method of claim 7 wherein the stepof extending the dosing tube pour end away from the pressure chambercomprises extending the first and second sections of the dosing tube,and providing a bellows sealing element around the first section and thedosing tube opening in the pressure chamber.
 13. A method of discharginga dose of molten metal from a pressure pour furnace, the methodcomprising the steps of: venting a pressure chamber of the furnace toatmospheric pressure; opening a sealing port disposed in a wall betweenthe pressure chamber and a heating chamber of the furnace by removingthe end of a sealing tube from an opening in the sealing port to allowthe flow of the molten metal from the heating chamber through thesealing port to the pressure chamber, the opening in the sealing portdisposed in the pressure chamber; energizing a sealing tube closeactuator to initiate movement of the end of the sealing tube towards theopening in the sealing port; seating the end of the sealing tube in theopening in the sealing port to terminate flow of the molten metal fromthe heating chamber to the pressure chamber; substantially sealing thepressure chamber from atmospheric pressure; providing a dosing tubethrough a dosing tube opening in the pressure chamber, the dosing tubecomprising a first and second contiguous sections, the first sectiondisposed exterior to the pressure chamber and terminating in a dosingtube pour end, the second section disposed interior to the pressurechamber and terminating in a dosing tube supply end; injecting a pourgas into the volume above the surface of the molten metal in thepressure chamber to force the molten metal into the supply end of thedosing tube; sensing when the level of molten metal in the dosing tubehas reached a ready level to regulate the pressure of the gas tomaintain the level of molten metal in the dosing tube at the readylevel; indexing the sprue of a mold adjacent to the dosing tube pourend; extending the dosing tube pour end to the sprue of the indexedmold; injecting the pour gas into the volume above the surface of themolten metal in the pressure chamber at a mold fill profile gasinjection rate to force the molten metal out of the dosing tube pour endand into the sprue of the indexed mold to fill the interior volume ofthe mold; adjusting the gas injection rate to return the level of moltenmetal in the dosing tube to the ready level; and retracting the dosingtube pour end from the sprue of the indexed mold.
 14. The method ofclaim 13 further comprising the steps of forming the sealing port fromthe combination of a cylindrically-shaped elbow passage and aconically-shaped passage, and orienting the elbow passage so that themolten metal flows through the elbow passage in a substantiallyhorizontal path out of the heating chamber and a substantially verticalpath into the conically-shaped passage into the pressure chamber whenthe sealing element is removed from the conically-shaped passage. 15.The method of claim 13 further comprising the step of sensing the backforce loading on the sealing tube actuator to detect blockage in theopening of the sealing port as the end of the sealing tube moves towardthe sealing port.
 16. The method of claim 13 wherein the step of sensingwhen the level of molten metal in the dosing tube has reached a readylevel further comprises the step of injecting a melt pressure sensinggas into a melt pressure sensing tube having an end immersed in themolten metal in the pressure chamber to sense a melt pressure sensinggas bubble release from the immersed end of the melt pressure sensingtube corresponding to the level of molten metal in the dosing tubehaving reached the ready level.
 17. The method of claim 13 furthercomprising the step of passing a stream of pressurized air across thedosing tube pour end to dislodge molten metal after retracting thedosing tube pour end opening from the sprue in the mold.
 18. The methodof claim 13 wherein the step of extending the dosing tube pour end awayfrom the pressure chamber comprises the steps of extending a firstpartial section of the first section of the dosing tube from theremainder of the first section of the dosing tube, the first partialsection of the first section of the dosing tube terminating in thedosing tube pour end, and providing a bellows sealing element around thefirst partial section and the remainder of the first section of thedosing tube.
 19. The method of claim 13 wherein the step of extendingthe dosing tube pour end away from the pressure chamber comprisesextending the first and second sections of the dosing tube, andproviding a bellows sealing element around the first section and thedosing tube opening in the pressure chamber.